espionage (n.)

• counterespionage
• counterintelligence
• espial
• following
• intelligence
• looking
• lookout
• note
• notice
• observance
• observation
• reconnaissance
• regard
• respect
• shadowing
• sleuthing
• spying
• stakeout
• surveillance
• tailing
• trailing
• viewing
• watch
• watching
• wiretap